The purpose of this study is to gain an understanding of the excitatory portions of the nervous system and how it is influenced by hormonal events in men and women. To further understand the differences between genders, hormonal events will be reproduced in men by the administration of a single 1 mg dose of estradiol. We have demonstrated a difference in nerve activity in men as compared to women during exercise. Additionally, we have shown that during the two phases of the menstrual cycle in women, the nerve activity differed with it being greater during times of low estrogen levels.